Diamond bits having diamonds positioned in concentric circles on the drilling face

ABSTRACT

A DRILLING BIT HAVING DIAMONDS EMBEDDED IN THE DRILLING FACE, WITH THE DIAMONDS ARRANGED IN A PATTERN OF CONCENTRIC CIRCLES HAVING AXIS COINCIDING WITH THE AXIS OF THE BIT. ALL OF THE DIAMONDS IN A GIVEN CIRCLE WILL SUBSCRIBE A COMMON PATH IN THE FACE OF THE MATERIAL BEING DRILLED. A METHOF OF MANUFACTURE OF SUCH A BIT IS DISCLOSED, ALONG WITH A SPECIAL MOLD FOR PRACTING THE METHOD.

Sept. 20, 1971 R. FEENSTRA 3,605,923

DIAIIOND BITS HAVING nnumws rosrrxoxsn IN CONCENTRIC cmcnas on wasDRILLING nos.

2 Shoots-Shoot} Original Filed March 6, 1 967 FIG. 2

I VII/I 9 9 FIG. 3

no u IO l0 u VJ'I/ mvsmon:

. .43" '4 b$ ROBIJN FEENSTRA h. #E'ENSTRA DIAMOND BITS HAVING DIAMONDSPOSITIONED IN CONCEN'I'RIC Sept. 20, 1971 3,605,923

CIRCLES ON THE DRILLING FACE- Original Filed March 6, 1967 2Sheets-Sheet 3 III. M WNANNN R MIN/aw FIG. 5

INVENTOR'.

ROBIJN FEENSTRA 5 #15 HIS AGENT United "States Patent 3,605,923 DIAMONDBITS HAVING DIAMONDS POSITIONED IN CFONCENTRIC CIRCLES ON THE DRILLINGFAC Robijn Feenstra, Rijswijk, Netherlands, assignor to Shell OilCompany, New York, N.Y.

Original application Mar. 6, 1967, Ser. No. 620,839. Divided and thisapplication Jan. 24, 1969, Ser. No. 813,352

Int. Cl. E21b 9/36 US. Cl. 175-329 7 Claims ABSTRACT OF THE DISCLOSURE Adrilling bit having diamonds embedded in the drilling face, with thediamonds arranged in a pattern of concentric circles having axescoinciding with the axis of the bit. All of the diamonds in a givencircle will subscribe a common path in the face of the material beingdrilled. A method of manufacture of such a bit is disclosed, along witha special mold for practicing the method.

This application is a divisional application of my copending applicationSer. No. 620,839, filed Mar. 6, 1967.

Diamond bits are in particular applied when drilling holes through rockmaterial of poor drillability, which is often required when drilling insubsurface formations for searching and/or recovering oil or othervaluable products.

These bits are of the rotary type and the diamonds thereof exert ascraping action on the rock through which a hole is being drilled, whilethe bit is loaded in an axial direction and rotated around its centralaxis.

Bits of this type are especially useful for drilling through deep,abrasive, hard formations, since their lifetime when drilling throughsuch formations is greater than with any other type of rotary rock bitsuch as a roller bit. Consequently, a diamond bit has to be replacedless frequently than a bit of another type. The higher material andmanufacturing costs of a diamond bit with respect to other types of bitsare easily compensated by the advantages obtained as a result of thereduction in time required to replace the worn bits during drillingoperations.

The invention is concerned with the provision of a sintered diamonddrilling bit which will be less liable to damage of the diamonds due tooverload than known bits.

The invention of said copending application is also concerned with amethod of manufacturing a sintered diamond drilling bit, in whichseveral steps are taken to insure that the arrangement of the diamondsin the sintered bit body is as accurate as possible, in order to dividethe load on the bit as evenly as possible over all the diamonds.

A further object of the invention is the provision of a sintered diamonddrilling bit, in which an extremely small number of diamonds is requiredfor carrying out the required cutting action.

The method of manufacturing a sintered diamond bit according to theinvention of said copending application comprises the following steps;

(a) Forming a graphite mold by placing a mixture of graphite particlesand liquid into a cup-shaped flexible membrane, introducing a pattern ofthe bit in an opening provided in a plate arrangement at the open sideof the cup-shaped membrane, such that the rim of the opening fitsclosely around the circumference of the pattern, densifying the mixtureby pressing part of the liquid out of the mixture by providing a fluidpressure on the outer Patented Sept. 20, 1971 side of the membrane,reducing the fluid pressure to atmospheric pressure, retracting thepattern out of the opening, and removing the graphite mold out of themembrane;

(b) Vaporizing the remaining part of the liquid from the graphite mold;

(c) Placing diamonds in the mold along circles which have their centerson the central bit axis, filling the mold with a mass of powder materialto be sintered, and placing a quantity of binder material on top of themass;

(d) Subjecting the mold with the contents thereof to sinteringtemperature, and

(e) Removing the sintered diamond bit from the mold after the sinteringprocess is over.

With this process it is possible to insure that the distances betweenthe central bit axis of the diamond bit and the cutting tops of thosediamonds located on a common circle vary at most 0.1 millimeter, whenmeasured in directions rectangular to the bottom profile to be cut bythe bit.

A means for carrying out part of the method according to the inventionof said copending application, comprises a housing open to one side, aplate member provided with an opening therein arranged on the open sideof the housing, a flexible membrane sealingly connected at the rimthereof to the open end of the housing, and means for connecting thespace between the housing and the membrane to a pressure source.

The invention may be carried into practice in various ways but twospecific embodiments will not be described by way of example withreference to the accompanying drawings in which:

FIG. 1 shows a view of the cutting end of a sintered diamond bitaccording to the invention taken in the direction of the axis in FIG. 2;

FIG. 2 shows a cross-section of this bit on the line 22 of FIG. 1;

FIG. 3 shows cross-sections of ridges of the bit on a larger scale;

FIG. 4 shows cross-sections similar to those shown in FIG. 3, but withridges of different form, and

FIG. 5 shows a molding apparatus for forming a graphite mold of thedrilling bit, which mold is to be used in the sintering process.

As shown in FIG. 2 the drilling bit 1 comprises a shank 2 provided withcoupling means, such as screwthread 3, for coupling the bit via a sub(not shown), to a drill string. The shank 2 is connected to a sinteredmass 4, which is provided with ridges 5, arranged as shown in FIG. 1,radially with respect to the central axis of the bit. A conduit 6 isarranged in the sintered body 4, which conduit communicates with thecavity 7 of the shank 2 for passing drilling fiuid out of the drillstring to the lower side of the bit 1 during drilling operations carriedout thereby.

Diamonds 8 are placed in the ridges 5 in such a way that the diamondsare located on circles which have their centers on the central bit axis.Preferably each diamond 8 forms together with diamonds 8 arranged inother ridges 5, a set of diamonds which is arranged on a common circle.By way of example, FIG. 3 shows cross-sections of three ridges 5 at thelocations of diamonds belonging to a common circle.

As will be seen from the following description of the method ofmanufacturing the present drill bit, the diamonds are arranged duringthe manufacturing of the bit on the bottom of channels provided in agraphite mold, which mold is subsequently filled with a mass of powdermaterial suitable to be sintered at a suitable temperature to a singlebody by the addition of a binder material. Thus, the diamonds 8 will, asshown in FIG. 3, contact the lower boundaries of the ridges 5.

During the drilling operation of a bit having diamonds 8 arranged inridges as shown in FIGS. 1-3, each set of diamonds located on a commoncircle will cut the formation along a common track. An equaldistribution of the load over the diamonds equally spaced along a commoncircle is only possible if the distances D between the central bit axisA-A and the cutting tops of the diamonds belonging to a common circleare, when measured in directions perpendicular to the bottom profile tobe cut by the bit, are equal to each other. It will be clear that thisis impossible due to the nature of the processes, which have to befollowed in manufacturing the bit. By applying the method according tothe invention, however, these distances D will vary within extremelysmall toler ances. In fact the maximum variation in these distances willbe at most 0.1 millimeter. Thus, in the bits according to the inventionthe diamonds equally spaced along a common circle and cutting in asingle track will be substantially equally loaded. Consequently, nooverload of diamonds will occur, which overload would normally result ina consecutive breaking of the diamonds, unless the total load on the bitwas reduced, which would, how ever, cause a reduction in penetrationrate of the bit.

In using the bit according to the present invention, however, the loadis evenly distributed over all the diamonds arranged in the bit, whichallows the maximum load to be applied to each diamond. Thus, aconsiderable penetration rate can be obtained with a minimum number ofdiamonds.

The number of diamonds belonging to a common circle need not be equal tothe number of ridges. In a bit hav' ing nine ridges, the diamonds maye.g. be placed on common circles containing 1, 3 or 9 diamonds, whichare evenly distributed with respect to the bit axis.

In the bit manufactured according to the present method, the distancesbetween corresponding points of the ridges of the bit axis AA vary atmost 0.05 millimeter when measured in directions perpendicular to thebottom profile cut by the bit.

The penetration rate can even further be improved by arranging thediamonds 10 in the manner indicated in FIG. 4. Ridges 11 are used, whichinstead of having flat bottoms have bottoms consisting of a portion 12,and a portion 13 arranged at an angle to the portion 12. It will beclear, that if the channels applied in the graphite mold in which thebit is to be sintered, have bottom portions 12 and 13 identical to thoseshown in FIG. 4, the diamonds 10 which are placed in these channels willcontact, provided that they are neither too great nor to small, bothportions 12 and 13 in each ridge 11. Consequently, the contact points 14lying on bottom portions 12, will be less blunt than the contact points9 in the construction shown in FIG. 3. The width of the portions 12 hasto be chosen in relation to the dimensions of the diamonds 8 which areto be used. To this end, all the diamonds have to be within a certainsize range if they are to be applied to a bit having bottom portions 12of a certain width. If the dimensions of a diamond are too great, therewill be no contact point with the bottom portion 12 as indicated bydiamond 10' in ridge 11. If desired, the side walls of the ridges 5 maybe sloped in the way as indicated in FIG. 3 to give the ridge a widerbase and more strength.

It will be clear that the invention is not limited to the bit as shownin FIGS. l4 of the drawing and that several modifications may be made.Thus, the ridges 5 (or 11) need not be arranged radially with respect tothe central bit axis as shown in FIG. 1, but they may also be arrangedsuch that in the view taken along the axis toward the bottom, they toucha common circle which has its center on the central bit axis. Furtherthese radially arranged ridges may be curved. In another embodiment theridges may be arranged more or less concentrically with respect to thebit axis.

Although the flushing conduit 6 has been shown in H6. 1 to be arrangedconcentrically with respect to the central axis of the bit 1, thisconduit may as well be placed eccentrically, which may be desirable forexample when no core should be left in the rock which is being drilled.

The shape of the bit body parts lying between the ridges 5, may be inany convenient way provided that it is suitable for guiding the flow offlushing liquid out of the opening 6 towards the sides of the bit bodyand along the diamonds 8, as well as for enabling an easy removal of thechips cut by the action of the diamonds 8. Further, the invention is notlimited to the shape of the shank 2, which shank is used for connectingthe bit to a drill string via a sub. If desired, the shank 2 may have acylindrical form. In another manner, several small cylinders arearranged in the body 4, which cylinders are provided with screw threadedopenings for connecting a flange thereto by means of bolts. The flangemay be provided with means for coupling the same to a drill string,drill collar or sub, or may form part of these latter means. A verysuitable manner of mounting the shank 2 in the body 1 has been shown incopending US. application 594,839, filed Nov. 16, 1966.

The method of manufacturing a sintered diamond bit will now bedescribed. To obtain the required accuracy in the setting of thediamonds, a special molding technique has been developed to form thegraphite mold in which the bit is to be sintered. An apparatus in whichsuch a technique may be carried out is shown in FIG. 5 of the drawing.The molding apparatus comprises a housing 21 having a cup-shapedinterior which is open at its upper side. A plate 22 provided with anopening 23 is arranged on the upper side of the housing and centered andsupported by the housing 21. A ring member 24 is connected to thehousing 21 by suitable means, such as bolts 25 for clamping a flexiblemembrane 26 (e.g. manufactured of rubber or other similar material) tothe housing 21.

On the housing 21 and the plate 22 there is mounted a bridge member 27by means of bolts 28 (of which only one is shown) which bolts arearranged in a flange 29 of the bridge member 27 and the vertical wall ofthe housing 21.

A rod 30 is provided with a flange 31 on which a pattern 32 of the bitto be manufactured is connected by bolts 33. The rod 30 is slidablyarranged in the bridge member 27, and rotation thereof is prevented by aslide wedge 34 connected to the flange 31 by a bolt 35 and cooperatingwith a guide member 36 connected to the bridge member 27 by bolts 37.

The rod 30 can be moved vertically with respect to the bridge member 27as well as to the housing 21 on which the bridge member 27 has beenmounted, by rotation of a nut member 38 cooperating by screw threadswith the bridge member 27. The nut member 38 is locked in an axial sensewith respect to the rod 30 and can be freely rotated therearound.

On the inner wall of the housing 21 a network of shallow channels 39 isarranged with at least one point thereof communicates via a bore 40 witha pressure source (not shown). Bore 40 passes through the wall of thehousing 21, and suitable conduits 41 communicate with the channels 39,and with the bore 40 leading the pressure source.

If desired, the membrane 26 may be flat in the nonstressed condition. Bylowering the pressure in the bore 40 to below atmospheric pressure, themembrane will be pressed against the inner wall of the housing 21 in theposition as shown in FIG. 5. The pressure source (not shown)communicating with the conduit 40 is then of a type which can producepressures higher as well as lower than atmospheric pressure.

To obtain in the graphite mold an exact negative form of the bit to bemanufactured, a pattern of the bit is made, which pattern has exactlythe same exterior shape (ridges 5, channel 6) as the bit shown inFIG. 1. For sake of simplicity, however, only the channel 6 has beenshown in the pattern 32 in FIG. 5. The pattern 32 is preferably made ofmetal, and has been machined very carefully. The variation in thedistances between the central axes of the pattern and the places on theridges where (in the bit) the diamonds which are to cut a common track,are to be located is maximum 0.02 millimeter when measured in adirection perpendicular to the bottom profile of the pattern.

In the position as indicated in 'FIG. 5, the pattern 32 fits accuratelywith its upper end in the opening 23 in the plate 22 without, however,sealing this opening. Suitable channels and conduits (such as 42, 43,and 44) are provided in the plate 22, pattern 32 and beteewn pattern 32and flange 31 respectively for draining the liquid which is pressed outof the liquid/ graphite mixture which will finally form the graphitemold 45.

In the particular pattern 32 indicated in the drawing, the lower innerpart has been conically shaped. It will, however, be clear that themethod according to the invention is not limited to the use of a type ofpattern as shown in the drawing, but may be applied for any otherpattern as well. If desired, other channels than channel 6 may beprovided in the pattern 32. These channels will, in the sintered bitbody, act as flushing channels for guiding the flow of drilling fluid tothe required parts of the bit and/or the hole. Since the shape andarrangement of such flow channels is known per se and do not form partof the invention, these channels are not described in detail. It isnoted, however, that the channels arranged in the pattern 32 have to beshaped such that the pattern can be easily removed out of the graphitemold after the molding operation is over, which removal should notdamage the channels formed in the mold by the ridges on the pattern 32.

The method of forming a graphite mold by means of the apparatus as shownin the drawing, will now be described in detail.

With the bridge member 27 and the pattern 32 removed from the housing21, the space inside the cupshaped flexible membrane 26 is partiallyfilled with a mixture substantially consisting of graphite particles andliquid, such as water. Thereafter the bridge member 27 having thepattern 32 either in the extended position, or in some other position,is placed on the housing 21 and connected thereto by the bolts 28. Ifthe pattern 32 is in the non-extended position with respect to thebridge member 27 when the latter is mounted on the housing 21, thepattern is moved into the position as indicated by FIG. 5 by rotation ofthe nut 38.

Subsequently, a fluid, preferably oil, is supplied under pressure from asuitable (not shown) pressure source via the conduits 40 and 41 to thechannels 39 arranged in the inner wall of the housing 21. By the networkof channels 39, the fluid is initially distributed over the surface ofthe membrane 26, thereby exerting compression forces on thegraphite/liquid mixture arranged within the membrane 26. By this action,part of the liquid is displaced from the mixture and drained viaconduits 42, 43, 44 and the narrow gap present between the wall of theopening 23 and the pattern 32, which gap allows the passage of water andair, but prevents the passage of graphite particles. The mixture isthereby densified.

The pressure exerted on the outer side of the membrane 26 should be asconstant as possible. If a pump is used for raising the pressure of thefluid, care has to be taken that the variations in pressure arerelatively small, say only 5% of the average pressure. It is preferred,however, to use a pressurized gas stored in a gas bottle, as a pressuresource. 'If desired, this gas may be supplied directly to the spacebetween the membrane 26 and the housing 21, or it may be applied to avessel containing a liquid, which vessel communicates at its lower endvia a conduit to the said space.

If the variations in pressure are too great, the graphite particles willnot be evenly compressed, which results in deviations in the mold withrespect to the pattern 32,

which deviations unfavorably affect the life time of the bit sintered insaid mold.

It has been found that the most homogeneous structure of the graphitemold will be obtained, if the pressure rise preceding the pressurizingperiod of the operation takes place very quickly, preferably within afew seconds.

The length of the period over which the mold is subjected to compressiveforces is determined experimentally for each mixture. The compressionperiod is over after maximum densification of the mixture has beenreached, and no more liquid escapes from the above-mentioned conduits42, 43, 44 and the narrow gap between the opening 23 and the pattern 32.

Thereafter the pressure is removed from the outside of the cup-shapedmembrane 26, and the pattern 32 is carefully lifted and retracted fromthe opening 23 by rotating the nut 38. This will only be possible if theparts of the pattern 32 have been designed such that they are slightlyconical in downward direction, and will, during upward movement of thepattern easily free themselves from their corresponding parts of themold without damaging them.

After the pattern 32 has been lifted through the opening 23, the bridgemember 27 and the plate 22 are removed and the graphite mold 45 isremoved from the housing 21, such as for example, by loosening the ringmember 24 and lifting the membrane 26 together with the mold 45 from thehousing 21, or by inverting the housing 21 together with the mold or byinjecting fluid via the conduit 40. If the membrane 26 is of the typewhich is flat in the non-stressed condition, the mold will be liftedfrom the housing 21 by the elasticity of the membrane 26.

The remaining part of the water, which has not been removed by thepressurizing operation of the mold is now removed therefrom, for exampleby drying the mold at ambient temperature or by exposing the mold to amoderate heating.

Thereafter the mold is ready for the sintering process. To this end,diamonds are carefully placed along circles in the channels which havebeen produced in the mold by ridges of the pattern 32. Due to themolding process according to the invention, the mold is a very accuratenegative of the pattern 32.

By the application of small quantities of adhesive material, thediamonds are kept in place with the powder material suitable to besintered is introduced into the mold. If desired, a shank suitable forconnecting the sintered bit to a drill string, etc., is placed in themold (compare for example FIG. 2, which shows the position of the shank2 with respect to the bit body 4, consisting of the sintered mass).

The shank 2 may be made of a material which has the same or about thesame expansion coefficient as the powder to be sintered. Hereby,undesirable stresses within the mass to be sintered, as well as withinthe mold, which would occur as a result of the temperature changesduring the sintering process, are prevented. Such stresses would distortthe bit contour, thus displacing the diamonds in such a way that theload exerted on the bit during drilling will be unevenly distributedover the diamonds.

The powder mass to be sintered may consist of tungsten and tungstencarbide, and the shank 2 may be formed by tungsten, either in solid formor in powder form. The shank 2 may be sintered to the tungsten. Thescrew thread 3 is to be out after the sintering process.

If the shank 2 is formed by a powder mass, a graphite mold (not shown)may be used for forming the outer surface of the shank. The screw thread3 may be formed on this latter graphite mold or may be cut on the shanklater on.

The shank 2 is preferably mounted in an annular groove which is formedin the sintered body 4, whereafter the shank 2 is brazed to the body 4,preferably by the process described in co-pending US. patent application594,839, filed Nov. 16, 1966.

Before placing the mold together with the diamonds and the powder to besintered into a sintering oven, an amount of binder material (such asGerman silver when sintering tungsten and/or tungsten carbide powder) isplaced in the powder material. To prevent distortion during the coolingprocess following the sintering process, it has been found that theamount of binder material must not be greater than the volume of thepore space of the powder mass. If greater amounts of binder material areapplied, the binder material remains in liquid form on top of the powdermaterial and solidifies in situ thereby causing distortion of the bitbody, which results in an uneven load distribution over the diamondswhen the bit is rotated under load when drilling a hole through rockmaterial.

If desired, the graphite mold may be strengthened by supporting it atthe outer side thereof, e.g. by placing it in a cup-shaped supportingmember, which member may be made of graphite. Preferably there is used agraphite cup, which is made of a solid block of graphite, for example byturning it on a lathe. If required, the outer side of the graphite moldis brought into a form to match the interior wall of the cup-shapedsupporting member by scraping any undesired graphite therefrom.

Strengthening of the mold by inserting reinforcements in thegraphite/liquid mixture before pressurizing it, is consideredunattractive since this may give rise to distortions of the mold duringthe manufacturing process and/ or during the sintering process.

The invention is not limited to a particular shape of the interior ofthe housing 21, and/or of the member 26. This latter need not be flat inthe non-stressed condition. The housing, or the membrane is pre-formed,is preferably symmetrical with respect to the central axis thereof andhas a cross-section as indicated in FIG. of the drawing. Preferably, thecentral axes of the pattern 32 and the housing 21 coincide.

The graphite mold, optionally supported by a cupshaped member, andcontaining diamonds, powder material, binder material, and optionally ashank for coupling purposes, after being placed in the sintering oven isheated to a temperature suitable to sinter the powder material to acommon unit, without burning the diamonds. As such processes are knownper se, no details need to be given here, regarding the sinteringtemperatures and sintering periods required for the various types ofsinter material and binder material, which may be applied.

By way of example, some details will be given of a molding and sinteringoperation of a 6" diamond bit. The bit had a shape corresponding to theshape of the pattern 32 as shown in FIG. 5. The membrane 26 had adiameter of about 210 millimeters, was about 1 millimeter thick and wasmade of rubber. The deviations of the tops of the ridges 5 (FIG. 1) onconcentric circles (along which the diamonds are to be placed) weremeasured, and the greatest variation occurring in the distances betweenthese tops and the centrol axis of the pattern 32 (FIG. 5), measured ina direction perpendicular to the bottom profile to be cut by a bitaccording to pattern 32, was 0.02 millimeter.

A mixture consisting of 60% graphite particles and 40% water wasmanually introduced in the membrane 26. Thereafter, the pattern 32 wasclamped in the position as indicated in the drawing, and oil underpressure was supplied to the channel 40. Within 5 seconds the pressurewithin the space bounded by the membrane 26 and the inner wall of thehousing 21 was raised from 1 to 30 kilograms per square centimeter,which latter pressure was applied over a period of 120 minutes duringperiod water was pressed out of the mixture and the mixture wasdensified. Thereafter, the pressure was brought down to 1 kilogram persquare centimeter. Subsequently, the pattern 32 was retracted from thegraphite mold and the plate 22 and the ring member 24 were removed so asto enable the lifting of the mold 45 from the apparatus.

After removal of the graphite mold the remaining part of the watercontained within the pores of the graphite mold was removed by heatingthe mold gradually over a period of 40 hours from ambient temperature to120 C. The mold was thereafter cooled down slowly. Eventually thisdrying may take place in the sintering oven by slowly heating up themold containing the diamonds, sintering mass and binder.

The diamonds used in this particular bit were between and carat andapplied in channels of the mold which had the shape of the ridges 11shown in FIG. 4. The width of the portions 12 was 0.8 millimeter.

After the diamonds had been glued in place by a suitable adhesive, amass of tungsten carbide powder was poured into the mold. Subsequentlyan amount of 3 kilograms German silver was added on top of the mass andthe mass was heated in an inert atmosphere up to a temperature of 1120C. over a period of 2.5 hours. Subsequent cooling down of the sinteredmass to room temperature took 12 hours.

Thereafter, the sintered bit was placed on a measuring stand, formeasuring the greatest variation in the distances between the cuttingtops of diamonds belonging to a common circle and the central axis, whenmeasured in a direction perpendicular to the bottom profile to be cut bythe bit. The greatest variation was 0.1 millimeter. The variation was0.05 millimeter or less for about of the diamonds.

The method according to the invention of said copending applicationallows the manufacture of graphite molds suitable for sinteringpurposes, which molds have dimensions which are so close to the designdimensions, that the diamonds which are applied in the various channelsformed by the ridges of the pattern 32 before the sintering material isapplied to the mold, have in the sintered bit such a mutual positionthat the load is evenly distributed over all the diamonds which arearranged over the ridges 5 and equally spaced along the circles whichhave their centers on the central bit axis. The drawback of an unevenload distribution over the diamonds which results in a breaking out ofthe diamonds one after the other is thereby prevented.

It will be clear that the present invention is not limited to theexample given but that various alternatives may be applied in themolding and sintering process, as well as in the constructive details ofthe bit.

I claim as my invention:

1. A sintered diamond drilling bit comprising:

a sintered, hard, wear-resistant body member having an upper portion andlower portion;

a shank member extending from the upper portion of said body member;

axially extending conduit means through said body member and said shankmember;

cutting means extending from the lower portion of said body member;

said cutting means comprising a plurality of ridges formed on the lowerportion of said body member; and

a plurality of diamonds at least partially embedded in each of saidridges and having at least a portion thereof exposed, said diamondsbeing positioned in a plurality of concentric common circles ofdiffering diameters whose centers coincide with the axis of said bodymember, the lower parts of each of the diamonds in any given circlelying in a common plane or conical surface, whereby all of the diamondsin any given circle subscribe a common path as the bit rotates in theface of the material being drilled.

2. A diamond drilling bit according to claim 1 wherein the ridges extendalong straight lines passing through the central axis of the bit.

3. A diamond drilling bit according to claim 1 wherein the conduit meansis centered about the central axis of the bit.

4. A diamond drilling bit according to claim 1 wherein the shank memberis of a different material than that of said body member and includesmeans for securing the bit to the lower end of drill string means.

5. In a diamond drilling bit of the type having a body with an uppershank for connection to the lower end of a rotary drill string and alower face for engaging the material at the bottom of a borehole, and aconduit extending in an axial direction through the body for passage ofdrilling fluid: a substantial portion of the material of the bodyadjacent said lower face being a sintered, hard, wear-resistantmaterial; a plurality of ridges formed in said lower face and extendingdownwardly from said lower face, the ridges forming a pattern on thelower face radiating generally outwardly from a central part thereof andproviding cutting means for engagement with the bottom of the borehole;a plurality of diamonds at least partially embedded in each of saidridges and each diamond having at least a portion thereof exposed at thelower-most part of the ridge, the diamonds being positioned in aplurality of concentric circles of differing diameters with the centersof the circles coinciding with the central axis of the body, whereby allof the diamonds in a given circle will subscribe a common path in thematerial drilled at the bottom of the borehole, the diamonds beingpositioned such that the lowermost part of each of the diamonds in agiven circle will be in a common plane or conical surface with that ofall of the other diamonds in each circle so that none of the diamondswill receive preferential wear or stress while engaging the bottom ofthe borehole.

6. In a diamond drilling bit according to claim 5, the ridges beingarranged along straight radial lines converging at the central axis ofthe body.

7. In a diamond drilling bit according to claim 5, the lower face of thebody being composed of sintered tungsten or mixture of tungsten andtungsten carbide, along with a binder material.

References Cited UNITED STATES PATENTS 2,264,617 12/1941 Carpenter etal. -329 2,371,490 3/1945 Williams, Jr. 175-329 2,493,178 1/1950Williams, Jr. 175329 3,112,803 12/1963 Rowley 175-329 3,135,341 6/1964Ritter 175329 JAMES A. LEPPINK, Primary Examiner

